1. Field of the Invention
The present invention relates to a III-V group compound semiconductor substrate containing nitrogen as its main component, and a method for producing the same. More specifically, the present invention relates to a III-V group compound semiconductor substrate containing nitrogen as its main component, preferably used as a substrate of a light-emitting element, and a method for producing the same.
2. Description of the Related Art
In recent years, blue light-emitting diodes with high brightness have been commercialized, utilizing a GaN compound semiconductor as a material for a light-emitting layer. Therefore, there has been growing interest in a nitride semiconductor as a material for a light-emitting device. Conventionally, a nitride semiconductor is grown by using a hydride vapor phase epitaxy method (hereinafter, referred to as an xe2x80x9cHVPE methodxe2x80x9d), metal organic chemical vapor deposition (hereinafter, referred to as an xe2x80x9cMOCVD methodxe2x80x9d), and a molecular beam epitaxy method (hereinafter, referred to as an xe2x80x9cMBE methodxe2x80x9d). It is preferable that a substrate on which crystal is grown is made of substantially the same material as that for a film to be grown on the substrate. More specifically, it is preferable that a nitride semiconductor is grown on a nitride single crystal substrate. However, it is difficult to obtain a nitride single crystal substrate with a large scale, so that a sapphire substrate (Japanese Laid-open Publication Nos. 2-229476 and 4-297023), an SiC substrate (Japanese Laid-open Publication No. 8-203834), a spinel substrate, a GaAs substrate, and the like have been used in the past.
As described above, in the case where a sapphire substrate is used as a substrate on which a nitride semiconductor is grown, there is an advantage that a sapphire substrate with high purity is easily available. However, there are disadvantages that a sapphire substrate and a nitride semiconductor grown on the substrate have lattice mismatching, and the difference in thermal expansion coefficient therebetween is large. Due to these disadvantages, a lot of defects of about 1010 cmxe2x88x922 are caused in a growth layer of a nitride semiconductor, and furthermore, potential stress is generated in the growth layer.
In the case where an SiC substrate is used as a substrate on which a nitride semiconductor is grown, the increase in defects caused by the lattice mismatching can be relaxed. However, the problem of potential stress caused by the difference in thermal expansion coefficient remains unsolved, which results in cracks on the surface of a growth film.
Furthermore, in the case where a GaAs substrate is used as a substrate on which a nitride semiconductor is grown, a crystal growth temperature is limited to a temperature for generating a GaAs layer. Thus, a crystal growth temperature in the vicinity of 1000xc2x0 C. required for growing a nitride semiconductor layer cannot be used. If semiconductor crystal is grown at such a low temperature, a growth film is likely to assume a configuration including cubic crystal and hexagonal crystal. This makes it difficult to grow good quality crystal.
A compound semiconductor substrate of the present invention, includes: a mica substrate; and a III-V group compound semiconductor layer containing nitrogen as its main component grown on the mica substrate.
In one embodiment of the present invention, the above-mentioned compound semiconductor substrate further includes an intermediate layer between the mica substrate and the III-V group compound semiconductor layer.
In another embodiment of the present invention, the above-mentioned compound semiconductor substrate further includes a mask pattern layer on a side of the mica substrate on which the III-V group compound semiconductor layer is grown.
In another embodiment of the present invention, the mica substrate is made of crystal having a composition of xcex11xe2x88x92xxcex23xe2x88x92y(xcex34O10)xcex42, wherein
Oxe2x89xa6xxe2x89xa60.5;
Oxe2x89xa6yxe2x89xa61;
xcex1 is selected from the group consisting of K, Ca, Na, Ba, NH4, and H3O;
xcex2 is selected from the group consisting of Al, Fe, Mg, Mn, Li, Zn, V, Cr, and Ti;
xcex3 is one or more element selected from the group consisting of Si, Al, Be, and Fe; and
xcex4 is F or OH.
In another embodiment of the present invention, the mica substrate is made of crystal having a composition of KMg3(Si3AlO10)F2.
In another embodiment of the present invention, the mica substrate is made of crystal having a composition of KMg3(Si3AlO10)(OH)2.
A method for producing a compound semiconductor substrate of the present invention, includes the step of growing a III-V group compound semiconductor layer containing nitrogen as its main component on a mica substrate.
In one embodiment of the present invention, the above-mentioned method for producing a compound semiconductor substrate further includes the step of providing an intermediate layer between the mica substrate and the III-V group compound semiconductor layer.
In another embodiment of the present invention, the above-mentioned method for producing a compound semiconductor substrate further includes the step of providing a mask pattern layer on a side of the mica substrate on which the III-V group compound semiconductor layer is grown.
In another embodiment of the present invention, the above-mentioned method for producing a compound semiconductor substrate further includes the step of peeling the mica substrate from the III-V group compound semiconductor layer.
In another embodiment of the present invention, the mica substrate is made of crystal having a composition of a xcex11xe2x88x92xxcex23xe2x88x92y(xcex34O10)xcex42, wherein
Oxe2x89xa6xxe2x89xa60.5;
Oxe2x89xa6yxe2x89xa61;
xcex1 is selected from the group consisting of K, Ca, Na, Ba, NH4, and H3O;
xcex2 is selected from the group consisting of Al, Fe, Mg, Mn, Li, Zn, V, Cr, and Ti;
xcex3 is one or more element selected from the group consisting of Si, Al, Be, and Fe; and
xcex4 is F or OH.
In another embodiment of the present invention, the mica substrate is made of crystal having a composition of KMg3(Si3AlO10)F2.
In another embodiment of the present invention, the mica substrate is made of crystal having a composition of KMg3(Si3AlO10)(OH)2.
In another embodiment of the present invention, the step of growing the III-V group compound semiconductor layer on the mica substrate includes the steps of: forming a mask pattern layer on the mica substrate; forming an intermediate layer in a region of the mica substrate where the mask pattern layer is not formed; growing a first III-V group compound semiconductor layer containing nitrogen as its main component on the intermediate layer by a first growth method; and growing a second III-V group compound semiconductor layer having the same composition as the composition of the first III-V group compound semiconductor layer on the first III-V group compound semiconductor layer by a second growth method, and the method further includes the step of peeling the mica substrate from the first and second III-V group compound semiconductor layers.
A light-emitting element of the present invention includes a semiconductor layered structure including at least a light-emitting layer on the above-mentioned III-V group compound semiconductor layer.
A method for producing a light-emitting element of the present invention includes the step of providing a semiconductor layered structure including at least a light-emitting layer on a III-V group compound semiconductor layer, wherein the III-V group compound semiconductor layer is produced during the above-mentioned step of growing the III-V group compound semiconductor layer.
According to the present invention, a compound semiconductor substrate including a III-V group compound crystal layer with high crystallinity containing nitrogen as its main component can be obtained by applying a mica substrate to a substrate for growing a III-V group compound semiconductor containing nitrogen as its main component.
In the mica substrate, generally, a ratio between binding force in a c-axis direction and binding force in a direction of a plane formed by an a-axis and a b-axis (hereinafter, referred to as an xe2x80x9cin-plane directionxe2x80x9d) is 1:about 10 to about 100, and defects are likely to be introduced in a layer in-plane direction. Furthermore, a ratio between binding force in a layer in-plane direction of a mica substrate and binding force of a III-V group compound semiconductor layer containing nitrogen as its main component is 1:about 10 to about 100. Therefore, even when stress (which is caused by the lattice mismatching between the mica substrate and the III-V group compound semiconductor layer containing nitrogen as its main component) is applied to the III-V group compound semiconductor layer containing nitrogen as its main component grown on the mica substrate, defects such as dislocations are introduced in a layer in-plane direction of the mica substrate to relax the stress. Because of this, a III-V group compound semiconductor layer with satisfactory crystallinity containing nitrogen as its main component can be obtained, in which the defects in a c-axis direction of the III-V group compound semiconductor layer containing nitrogen as its main component are suppressed, and dislocation density (defects) of GaN, AlN, AlxGa1xe2x88x92xN(0 less than x less than 1), InyGa1xe2x88x92yN(0 less than y less than 1) is small.
Furthermore, after a III-V group compound semiconductor layer containing nitrogen as its main component is grown on a mica substrate, the mica substrate can be easily removed from the semiconductor layer by peeling. Therefore, it is not required that a notch is previously provided in the mica substrate for the purpose of easily detaching the mica substrate. Moreover, a material for the mica substrate can be selected so as to have appropriate heat resistance, lattice constant, and/or thermal expansion coefficient, depending upon the purpose. Therefore, a III-V group compound semiconductor substrate containing nitrogen as its main component can be provided, which is suitable for producing a light-emitting element with suitable light-emitting characteristics.
Thus, the invention described herein makes possible the advantage of providing a substrate with high heat resistance in which the difference in a lattice constant and in a thermal expansion coefficient is relatively small between the substrate and the III-V group compound semiconductor containing nitrogen as its main component to be grown on the substrate and which allows a III-V group compound semiconductor layer containing nitrogen as its main component to be grown on the substrate at high temperatures, thereby obtaining good quality crystal of a III-V group compound semiconductor containing nitrogen as its main component.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.